Habitat Utilization and Behavioral Interaction of Juvenile Atlantic Salmon (Salmo salar) and Rainbow Trout (S. gairdneri) in Tributaries of the White River of Vermont

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Abstract
Competition for space between stocked juvenile Atlantic salmon, Salmo salar, and wild juvenile rainbow trout, S. gairdneri, was examined in stream channel experiments, a field experiment, and in field habitat surveys. In stream channels providing riffle and pool habitats, species differed in their distribution both as underyearlings (0+) and as yearlings (1+). Yearling salmon occurred more often in stream channel riffles during trials with 1+ rainbow trout than during trials testing only salmon; trout distributions in the channels were unaffected by salmon. In a field experiment conducted to determine if the stocking of 0+ Atlantic salmon causes the displacement of resident 0+ rainbow trout, salmon fry were stocked at a density of 85 per 100 m2. Emigration from the stocked zone and an unstocked control zone were then monitored daily with four weirs. The 0+ salmon had no apparent effect on the rate of movement of resident rainbow trout fry. During summer and fall field surveys, 0+ salmon occupied deeper and swifter water than 0+ rainbow trout; as yearlings these species occupied similar habitats. In late fall, segregation by habitat occurred: Atlantic salmon were primarily in riffles; rainbow trout were primarily in pools. We found no evidence of competition between cohorts of underyearlings; however, the niche shift by 1+ salmon in the stream channels suggested that, at times, juveniles of these species will compete for space.

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